The killer for me with Borderlands 2 was not being able to load a saved game and get back to where you were - you respawn at the nearest fast travel point, and have to make your way back through areas you've already been (and have to kill the same enemies again).

Not great when you have only small chunks of time to play the game in, and might not want to do a whole mission at a time.

I'm really surprised that this is hardly mentioned anywhere in reviews of B2.